1. Field of the Invention
The present invention relates, in general, to a method of fabricating a paste bump for a printed circuit board (PCB), and more particularly, to a method of fabricating a paste bump for a PCB, which enables the number of printings to be decreased, to thus reduce the fabrication cost and process time in the formation of the paste bump on the PCB.
2. Description of the Related Art
In order to realize high-density PCBs with the development of electronic components, there is a demand for techniques for improving the performance of HDI (High Density Interconnection) substrates to which the interlayer electrical connection of circuit patterns and micro-circuit wiring are applied. Specifically, improvement in the performance of the HDI substrate requires techniques for ensuring the interlayer electrical connection of circuit patterns and the freedom of design thereof.
Conventionally, a multilayer PCB is fabricated by forming inner circuits on the surfaces of a core substrate, for example, a copper clad laminate (CCL), through an additive method or a subtractive method, sequentially building up insulating layers and circuit layers, and forming outer circuits through the same method as for the inner circuits.
However, such a conventional process of fabricating the multilayer PCB does not satisfy requests for low costs due to a fall in the price of the application products thereof, including mobile phones, and for a reduction in lead-time to increase mass production, and thus a novel fabrication process that is able to solve these problems is required.
In order to simplify the complicated process of the prior art and to rapidly and inexpensively fabricate a multilayer PCB using a collective lamination procedure, so-called B2it (Buried Bump Interconnection Technology) has been commercialized, which allows simple and convenient lamination by printing a conductive paste on a copper foil to thus form bumps, and laminating an insulation element thereon to prefabricate a paste bump board.
FIG. 1 is a flowchart illustrating the process of fabricating a paste bump for a PCB according to a conventional technique, and FIG. 2 is a view illustrating the shape of the paste bump formed using the process of fabricating a paste bump for a PCB, as illustrated in FIG. 1, according to a conventional technique.
With reference to FIGS. 1 and 2, a base plate 100 on which a paste bump 200 is to be formed is prepared, after which a mask having a hole is placed on the portion of the base plate 100 at which the paste bump 200 is to be formed.
Next, a conductive paste is applied on the mask, and is then pressed using a squeegee so that the hole in the mask is filled with the conductive paste (S100).
As such, the conductive paste is stuck to the base plate by the pressure of the squeegee.
Next, the conductive paste printed on the base plate 100 is dried (S200).
Accordingly, as seen in FIG. 2, the paste bump 200 having a first height h1 is formed.
Because the conductive paste has high viscosity and low TI, printing and drying of the conductive paste are repeated 4˜5 times after a single printing of the conductive paste, thus forming the paste bump 200 having a predetermined height H.
In order to form a paste bump 200 having a desired height H through the method of fabricating the paste bump for a PCB according to a conventional technique, printing and drying of a conductive paste having high viscosity and low TI are repeated several times, and thereby the process time required to form the paste bump for a PCB is increased, undesirably decreasing productivity.
Further, because printing and drying of the conductive paste are repeated several times, the conductive paste, a large amount of which is placed in the hole in the mask, must be pressed upon printing of the conductive paste, undesirably increasing the fabrication cost required to form the paste bump for a PCB.